Field of the Invention
The invention relates generally to the art of axle/suspension systems for heavy-duty vehicles. More particularly, the invention relates to axle/suspension systems for heavy-duty vehicles which utilize an air spring to cushion the ride of the vehicle. More specifically, the invention is directed to an air spring with damping characteristics for a heavy-duty vehicle axle/suspension system, whereby the air spring utilizes multiple chambers connected via staged openings that provide better airflow control and promote damping of the axle/suspension system over a broader range of loads, wheel motions and frequencies utilizing a generally reduced air volume in order to improve ride quality for the heavy-duty vehicle during operation.
Background Art
The use of air-ride trailing and leading arm rigid beam-type axle/suspension systems has been very popular in the heavy-duty truck and tractor-trailer industry for many years. Although such axle/suspension systems are found in widely varying structural forms, in general their structure is similar in that each system typically includes a pair of suspension assemblies. In some heavy-duty vehicles, the suspension assemblies are connected directly to the primary frame of the vehicle. In other heavy-duty vehicles, the primary frame of the vehicle supports a subframe, and the suspension assemblies connect directly to the subframe. For those heavy-duty vehicles that support a subframe, the subframe can be non-movable or movable, the latter being commonly referred to as a slider box, slider subframe, slider undercarriage, or secondary slider frame. For the purpose of convenience and clarity, reference herein will be made to main members, with the understanding that such reference is by way of example, and that the present invention applies to heavy-duty vehicle axle/suspension systems suspended from main members of: primary frames, movable subframes and non-movable subframes.
Specifically, each suspension assembly of an axle/suspension system includes a longitudinally extending elongated beam. Each beam typically is located adjacent to and below a respective one of a pair of spaced-apart longitudinally extending main members and one or more cross members, which form the frame of the vehicle. More specifically, each beam is pivotally connected at one of its ends to a hanger, which in turn is attached to and depends from a respective one of the main members of the vehicle. An axle extends transversely between and typically is connected by some means to the beams of the pair of suspension assemblies at a selected location from about the mid-point of each beam to the end of the beam opposite from its pivotal connection end. The beam end opposite the pivotal connection end also is connected to an air spring, or other spring mechanism, which in turn is connected to a respective one of the main members. A height control valve is mounted on the main member or other support structure and is operatively connected to the beam and to the air spring in order to maintain the ride height of the vehicle. A brake system and, optionally, one or more shock absorbers for providing damping to the axle/suspension system of the vehicle also are mounted on the axle/suspension system. The beam may extend rearwardly or frontwardly from the pivotal connection relative to the front end of the vehicle, thus defining what are typically referred to as trailing arm or leading arm axle/suspension systems, respectively. However, for purposes of the description contained herein, it is understood that the term “trailing arm” will encompass beams which extend either rearwardly or frontwardly with respect to the front end of the vehicle.
The axle/suspension systems of the heavy-duty vehicle act to cushion the ride, dampen vibrations and stabilize the vehicle. More particularly, as the vehicle is traveling over the road, its wheels encounter road conditions that impart various forces, loads, and/or stresses, collectively referred to herein as forces, to the respective axle on which the wheels are mounted, and in turn, to the suspension assemblies that are connected to and support the axle. In order to minimize the detrimental effect of these forces on the vehicle as it is operating, the axle/suspension system is designed to react and/or absorb at least some of them.
These forces include vertical forces caused by vertical movement of the wheels as they encounter certain road conditions, fore-aft forces caused by acceleration and deceleration of the vehicle as well as certain road conditions, and side-load and torsional forces associated with transverse vehicle movement, such as turning of the vehicle and lane-change maneuvers. In order to address such disparate forces, axle/suspension systems have differing structural requirements. More particularly, it is desirable for an axle/suspension system to have beams that are fairly stiff in order to minimize the amount of sway experienced by the vehicle and thus provide what is known in the art as roll stability. However, it is also desirable for an axle/suspension system to be relatively flexible to assist in cushioning the vehicle from vertical impacts, and to provide compliance so that the components of the axle/suspension system resist failure, thereby increasing durability of the axle/suspension system. It is also desirable to dampen the vibrations or oscillations that result from such forces. A key component of the axle/suspension system that cushions the ride of the vehicle from vertical impacts is the air spring. In the past, a shock absorber was utilized on the axle/suspension system to provide damping characteristics to the axle/suspension system. More recently, air springs with damping characteristics have been developed that eliminate the shock absorber, and the air spring provides damping to the axle/suspension system. One such air spring with damping characteristics is shown and described in U.S. Pat. No. 8,540,222, owned by the assignee of the instant application, Hendrickson USA, L.L.C.
A conventional air spring without damping characteristics which is utilized in heavy-duty air-ride axle/suspension systems includes three main components: a flexible bellows, a piston and a bellows top plate. The bellows is typically formed from rubber or other flexible material, and is operatively mounted on top of the piston. The piston is typically formed from steel, aluminum, fiber reinforced plastics or other rigid material, and is mounted on the rear end of the top plate of the beam of the suspension assembly by fasteners of the type that are generally well known in the art. The volume of pressurized air, or “air volume”, that is contained within the air spring is a major factor in determining the spring rate of the air spring. More specifically, this air volume is contained within the bellows and, in some cases, the piston of the air spring. The larger the air volume of the air spring, the lower the spring rate of the air spring. A lower spring rate is generally more desirable in the heavy-duty vehicle industry because it provides a softer ride to the vehicle during operation.
Prior art air springs without damping characteristics, while providing cushioning to the vehicle cargo and occupant(s) during operation of the vehicle, provide little, if any, damping characteristics to the axle/suspension system. Such damping characteristics are instead typically provided by a pair of hydraulic shock absorbers, although a single shock absorber has also been utilized and is generally well known in the art. Each one of the shock absorbers is mounted on and extends between the beam of a respective one of the suspension assemblies of the axle/suspension system and a respective one of the main members of the vehicle. These shock absorbers add complexity and weight to the axle/suspension system. Moreover, because the shock absorbers are a service item of the axle/suspension system that will require maintenance and/or replacement from time to time, they also add additional maintenance and/or replacement costs to the axle/suspension system.
The amount of cargo that a vehicle may carry is governed by local, state, and/or national road and bridge laws. The basic principle behind most road and bridge laws is to limit the maximum load that a vehicle may carry, as well as to limit the maximum load that can be supported by individual axles. Because shock absorbers are relatively heavy, these components add undesirable weight to the axle/suspension system and therefore reduce the amount of cargo that can be carried by the heavy-duty vehicle. Depending on the shock absorbers employed, they also add varying degrees of complexity to the axle/suspension system, which is also undesirable.
An air spring with damping characteristics, such as the one shown and described in U.S. Pat. No. 8,540,222, owned by the assignee of the instant application, Hendrickson USA, L.L.C., includes a piston having a hollow cavity which is in fluid communication with the bellows via at least one opening, which provides restricted communication of air between the piston and the bellows volumes during operation of the axle/suspension system. The air volume of the air spring is in fluid communication with the height control valve of the vehicle, which in turn is in fluid communication with an air source, such as an air supply tank. The height control valve, by directing air flow into and out of the air spring of the axle/suspension system, helps maintain the desired ride height of the vehicle.
The restricted communication of air between the piston chamber and the bellows chamber during operation provides damping to the axle/suspension system. More specifically, when the axle/suspension system experiences a jounce event, such as when the vehicle wheels encounter a curb or a raised bump in the road, the axle moves vertically upwardly toward the vehicle chassis. In such a jounce event, the bellows is compressed by the axle/suspension system as the wheels of the vehicle travel over the curb or the raised bump in the road. The compression of the air spring bellows causes the internal pressure of the bellows to increase. Therefore, a pressure differential is created between the bellows and the piston chamber. This pressure differential causes air to flow from the bellows through the opening(s) into the piston chamber. Air will continue to flow back and forth through the opening(s) between the bellows and the piston chambers until the pressures of the piston chamber and the bellows chamber have equalized. The restricted flow of air back and forth through the opening(s) causes damping to occur.
Conversely, when the axle/suspension system experiences a rebound event, such as when the vehicle wheels encounter a large hole or depression in the road, the axle moves vertically downwardly away from the vehicle chassis. In such a rebound event, the bellows is expanded by the axle/suspension system as the wheels of the vehicle travel into the hole or depression in the road. The expansion of the air spring bellows causes the internal pressure of the bellows to decrease. As a result, a pressure differential is created between the bellows and the piston chamber. This pressure differential causes air to flow from the piston chamber through the opening(s) into the bellows chamber. Air will continue to flow back and forth through the opening(s) between the bellows and the piston chambers until the pressures of the piston chamber and the bellows chamber have equalized. The restricted flow of air back and forth through the opening(s) causes damping to occur.
Prior art air springs having damping characteristics have certain limitations due to their structural make-up. First, because the prior art air springs only include openings located between the bellows chamber and the piston chamber, the damping range of the air spring is typically limited to a particular load or wheel motion. These limitations on the damping range of the air spring limit the ability to “tune” the damping for a given application. Therefore, it is desirable to have an air spring with damping features that makes it possible to have a broader damping range over a broader range of loads and wheel motions, thereby expanding the operating range of the damping air spring.
Second, prior art air springs with damping characteristics typically provide maximum damping that is frequency dependent. This means that the maximum damping provided by the air spring at a frequency of 1 Hz can be greatly reduced at a frequency of 10 Hz. Therefore, it is desirable to have an air spring with damping features that reduces or eliminates frequency dependence.
Third, prior art air springs with damping characteristics typically require a large air volume. This large air volume requirement in turn increases the amount of space required by the axle/suspension system, which typically is not desirable in the heavy-duty vehicle industry, because increasing the amount of space required by the axle/suspension system increases weight and reduces the room allowed for payload, the result being that less payload can be carried by the vehicle. Therefore, it is desirable to have an air spring with damping features that makes it possible to reduce the need for larger air volumes to increase damping. This, in turn, enables use of a smaller air spring and reduces the amount of space required by the axle/suspension system, which allows more room and weight for payload or cargo.
The air spring with damping characteristics for heavy-duty vehicles of the present invention overcomes the problems associated with the prior art air springs with and without damping features, by providing an intermediate chamber with staged openings in fluid communication with the bellows chamber and the piston chamber that exhibits better airflow control, resulting in optimization of the damping characteristics of the air spring. By providing an air spring for heavy-duty vehicles having optimized damping characteristics, the shock absorber of the axle/suspension system can be eliminated or its size reduced, reducing complexity, saving weight and cost, and allowing the heavy-duty vehicle to haul more cargo. Moreover, elimination of the shock absorbers potentially eliminates costly repairs and/or maintenance costs associated with these systems.
The air spring with damping characteristics for heavy-duty vehicles of the present invention provides damping features to the axle/suspension system over a broader damping range to accommodate a broader range of loads and wheel motions, thereby reducing the constraints on the operating range of the damping air spring. In addition, the air spring with damping characteristics for heavy-duty vehicles of the present invention reduces or eliminates frequency dependence. Moreover, the air spring with damping characteristics for heavy-duty vehicles of the present invention makes it possible to reduce the need for larger air volumes to increase damping features, which in turn enables use of a smaller air sprig and reduces the amount of space required by the axle/suspension system and thus allows more room and weight for payload or cargo.